What you'll need
A tape measure for reachable walls, a laser measure for tall or steep ones (measuring from the ground beats a shaky ladder), a notepad or your phone, and a simple sketch of the house footprint. You'll record three kinds of surface: rectangular walls, triangular gables, and openings to subtract.
Step 1 — Measure each wall
Take every elevation separately: front, back, left, right, and any bump-outs. For each, measure the width and the height from the bottom of the siding to the eave (where the wall meets the roof overhang). Write them down as width × height. Don't average walls together — different heights and widths need their own lines.
Step 2 — Add the gables
Gable ends are the triangles under a pitched roof, and they're the most-forgotten surface. For each gable, measure the base (the full width at the eave line) and the rise (straight up to the peak). You don't need the sloped edges — base and rise give you the area, which is half of base times rise. Count every gable and dormer face.
Step 3 — Measure the openings
Record each window, door and garage door as width × height, and note how many of each size you have. These get subtracted from the wall area so you're not buying material to cover glass and doorways. Very small openings can be left in as part of the waste buffer, but capture the significant ones.
Step 4 — Add a waste allowance
No job uses siding with zero offcuts. Add about 10% for a simple rectangular house, and 12–15% when you have several gables, dormers, angled cuts or a diagonal pattern. The waste allowance is cheap insurance against a short order and a mismatched late delivery.
Step 5 — Convert and order
Add your wall and gable areas, subtract the openings, and divide by 100 to get squares — the unit suppliers quote from. From there, your material's coverage gives you panels or boards and boxes. The siding calculator does steps 5 and beyond automatically once you type in the numbers from your notepad.
Common mistakes to avoid
The big three: forgetting the gables entirely, measuring wall height to the roof peak instead of stopping at the eave and adding the gable separately, and skipping the openings so you over-order. Measure methodically, one surface at a time, and you'll avoid all three.
A simple measuring checklist
If you want a repeatable routine, work the house in this order and you'll never miss a surface. Start at the front-left corner and move clockwise so you don't lose track of which walls you've done. For each elevation, capture the rectangle first, then any triangle above it, then the openings within it — in that sequence, every time.
- Front elevation: main wall width × height, gable or dormer triangles, then windows, entry door and any porch openings.
- Right elevation: wall width × height, gable if the roof runs that way, then windows and side doors.
- Back elevation: wall width × height, gable or dormers, then windows, back door and patio doors.
- Left elevation: wall width × height, gable if present, then remaining windows.
- Attached structures: garage and bump-outs measured as their own walls, with the garage door subtracted.
Double-check totals by comparing opposite walls — front and back are often the same width, and the two sides frequently match. A number that's wildly different from its opposite is usually a transcription error worth re-measuring before you order.